Study on Optical and Mechanical Properties of Magnesium Based Composites Prepared by Magnetron Sputtering

磁控濺射製備鎂基復合薄膜材料的光學和力學性能研究

Student thesis: Doctoral Thesis

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Award date21 Jul 2020

Abstract

Among the magnesium-based materials, Mg-based metallic glass thin films (MGTFs) attracted great attentions due to their advantageous combination of high strength to weight ratio and low density and excellent biocompatibility. Mg-based MGTFs show excellent ratio strength and demonstrate great potential for biodegradable implants with the great reduction in hydrogen evolution and the same good tissue compatibility, for instance, the MgZn-based metallic glass demonstrate excellent capability in degrading azo dyes under complex environmental conditions. However, regarding optical properties, there is little work has been done on the color related optical properties of Mg-based MGTFs. In addition, in view of the Mg-based MGTFs composite material, there is also little attention to reveal the role it played in structural analysis and mechanical properties. In this thesis, considerable attention is given to two novel applications of Mg-based MGTFs. Detailed researches and result are listed as follows:

Full-color reflective filters for large area applications with potentially unprecedented color saturation and excellent mechanical properties deposited by one-step magnetron sputtering were proposed. Conventional reflective color filters with multiple layers of dielectric films could not simultaneously produce a large area and good mechanical properties due to the complex multiple depositions and the difference in the thermal expansion coefficients among the material layers. Herein, full-spectrum colors were generated by novel Mg-based reflective color filters in a large area of 2 cm × 2 cm with a high hardness of 9.12 GPa, where the filters include an absorber layer with controllable optical constants and a reflective layer with an amorphous structure. The saturation and hue of the produced colors can be controlled by tuning the optical constants and the thickness of the absorber layer. Additionally, the hardness of the Mg-based reflective color filters was increased by the reflective metallic glass layers because they were derived from the same material as the absorber layer. This paradigm could pave the way for the efficient fabrication of large area color filtering devices for diverse applications, such as surface decorations, optical components, color display devices, structural color printing and photovoltaic cells with optimum efficiency.

High-strength surface metalized polymer was prepared through magnetron sputtering followed by uniaxial stretching. The results indicated that the tensile strength of Mg-based MGTFs coated poly(ethylene terephthalate) (PET) mainly depended on the thickness of MGTFs. Moreover, the tensile strength of the surface metalized PET (55 MPa) was nearly 2 times higher than the uncoated PET (32 MPa) under an optimized condition. And the tensile stain of the surface metalized PET (1100 %) was almost 2 times higher than that of the uncoated PET (520%) and at least 10 times longer than the original PET. This is due to the synergistic effect between film coating and crystallization during stretching. After the polymer is uniaxially stretched, the long-chain molecular chains in the polymer are stretched and aligned along the stretching direction, that is, the phenomenon of strain-induced crystallization occurs. When the stretching continues, the molecular chains are not enough to support such a large strain, and breakage occurs, and then at the weaker molecular chains, the polymer breaks perpendicular to the stretching direction. When an amorphous film is deposited on the polymer surface, the film will generate uniform cracks perpendicular to the stretching direction, and then become a film fragment. The fragment has a strong binding force with the polymer, so that it will not fall off. When the position of the polymer covered by the amorphous film continues to be stretched, the molecular chain that originally tends to extend along the stretching direction is confined to the amorphous film with a strong specific strength, which in turn limits the polymer mechanical performance. The strain-induced crystallization tendency increases the overall tensile strength of the surface metallized polymer.

    Research areas

  • reflective color filters, interference effect, structural colors, absorber materials, metallic glass thin films, PET composite materials